The fact that soldiers of a foreign government ARE allowed to patrol their territory is good enough.

Its like if the US allowed chinese red guards patrol the streets of San Francisco "as long as they follow the law". Its simply a declarative surrender of their authority over their territory.

Foreign government agents enforcing openly their government policy in your territory is a blatant surrender of sovereignty, no matter how your slice it or rationalize it. And im goddamn sure the Thalmor knows it and openly Patrols Skyrim explicitly to further humiliate the Empire and Skyrim residents.